The Currently, the 3rd generation partnership project (3GPP) is standardizing a feature called Narrowband Internet of Things (NB-IoT) for satisfying the requirements of Machine Type Communication (MTC) applications, while maintaining backward compatibility with the current LTE radio access technology. Minimizing overhead in communication of control information, including uplink resource grants, and limiting inter-cell interference introduced by the transmission of payload data in a NB-IoT environment proves challenging because it may be necessary for NB-IoT devices to operate in environments that exhibit very low signal to noise ratios (SNRs) while being unable to leverage existing LTE techniques for interference mitigation minimizing overhead given the limited available uplink frequency bandwidth and processing power capabilities of NB-IoT devices.
In some current wireless communication systems, a network-side scheduler is able to schedule uplink transmissions for associated NB-IoT wireless communication devices with a 1-subcarrier granularity. As a result, separate cells or base stations may freely schedule uplink transmissions over any available uplink subcarrier or groups of carriers essentially without limitation. This leads to a large number of scenarios where neighboring cells or base stations schedule respective uplink transmissions that wholly or partially overlap in frequency and time, which can result in inter-cell interference. Some wireless communication systems counter this risk of interference by implementing multiple uplink transmissions in each cell for a number of wireless communication devices. The orthogonality between overlapping transmissions might be comprised. Some wireless communication systems counter this risk of interference by implementing a DMRS sequence in each cell and a phase shift to the cell DMRS for each wireless communication device in a cell, which can maintain orthogonality between overlapping transmissions where a sufficient number of device-specific DMRS code and phase shift combinations exist to cover all of the transmitting wireless communication devices in the system. However, when the granularity of uplink resource allocations is on the single-subcarrier level and the number of wireless communication devices in the system increases, an insufficient number of combinations may exist to ensure orthogonality between any device pair, resulting in potentially high correlation between device-specific combinations and increased inter-cell interference.
Therefore, techniques are needed for reducing the potential for inter-cell interference caused by uplink transmissions in narrowband communication systems, such as NB-IoT.